1. Field of the Invention
The present disclosure relates to a method of fabricating a display device, and more particularly, to a method of fabricating an organic light emitting diode display device where a flexible substrate is easily detached from a carrier substrate without using a laser apparatus and deterioration such as lift of an organic electroluminescent diode and generation of a bubble is prevented.
2. Discussion of the Related Art
Among various flat panel display devices (FPDs), an organic light emitting diode (OLED) display device has a relatively high brightness and a relatively low driving voltage. In addition, since the OLED display device has an emissive type emitting a light for itself, the OLED display device has a relatively high contrast ratio and a relatively thin profile. The OLED display device has an advantage in displaying moving images due to a response time of several microseconds. Further, the OLED display device has no limitation in a viewing angle and has stability even at a low temperature. Since the OLED display device is driven with a low voltage of direct current (DC) 5V to DC 15V, it is easy to design and fabricate a driving circuit. Moreover, since a deposition apparatus and an encapsulation apparatus are all that is needed for fabricating the OLED display device, the fabrication process for the OLED display device is very simple.
The OLED display devices are classified into a passive matrix type and an active matrix type. In the case of the passive matrix type OLED display device, since an organic electroluminescent (EL) diode is directly connected to a scan line and a signal line that cross each other to define a pixel region in matrix, the organic EL diode emits a light of instant brightness that equals to average brightness multiplied by the number of the scan line.
In the case of the active matrix type OLED device, a switching thin film transistor (TFT) is disposed in each pixel region and a driving TFT connected to the switching TFT is connected to the organic EL diode and a power line in each pixel region. The organic EL diode includes a first electrode connected to the driving TFT, a second electrode functioning as a common electrode and an organic emitting layer between the first and second electrodes. A voltage applied to the pixel region is stored in a storage capacitor and maintained until a signal for the next frame is applied. Accordingly, the pixel region can retain the signal until the next frame regardless of the number of the scan line. Because the active matrix type OLED display device can obtain a desired luminance with low current, the active matrix type OLED display device has advantages such as low power consumption, high resolution and large size and has been widely used.
Recently, the OLED display device is being fabricated using a plastic substrate of a thickness of about 10 μm to about 200 μm as a base substrate for maximizing flexibility. However, it is hard to maintain a flat state of the plastic substrate due to flexibility while the plastic substrate is transferred between unit processes and is disposed on a stage. Accordingly, when the OLED display device is fabricated using the plastic substrate, the plastic substrate is attached to an additional carrier substrate that is hardly bent and has a flat state on the stage and the carrier substrate is detached from the plastic substrate in a subsequent process to complete the OLED display device having excellent flexibility.
FIG. 1A to 10 are cross-sectional views showing a method of fabricating an organic light emitting diode display device according to the related art. In FIG. 1A, an ablation layer 7 is formed on a carrier substrate 5. The carrier substrate 5 includes a glass where a laser beam can pass. In addition, the ablation layer 7 includes hydrogenated amorphous silicon (a-Si:H) that can emit a hydrogen gas by irradiation of the laser beam to detach a plastic substrate from the carrier substrate 5.
In FIG. 1B, a plastic substrate 11 is formed on the ablation layer 7 by coating and heating a plastic material of a liquid state. In FIG. 1C, a gate line (not shown), a data line (not shown), a switching thin film transistor (TFT) (not shown) and a driving TFT DTr are formed on the plastic substrate 11. In addition, an organic electroluminescent (EL) diode E, which includes a first electrode 47 connected to a drain electrode of the driving TFT DTr, an organic emitting layer 55 and a second electrode 58, is formed on the driving TFT DTr. Further, a protecting sheet 80 for protecting the organic EL diode E is formed on the organic EL diode E and a module process for attaching a driving circuit board (not shown) is attached to the plastic substrate 11.
In FIG. 1D, a laser beam LB of a laser apparatus 99 is irradiated onto the ablation layer 7 through a rear surface of the carrier substrate 5. Since the hydrogen gas H of the hydrogenated amorphous silicon (a-Si:H) is erupted from the ablation layer 7, the plastic substrate 11 having the switching TFT, the driving TFT DTr and the organic EL diode E thereon is detached from the carrier substrate 5 to complete an organic light emitting diode (OLED) display device 70.
However, since the step of detaching the plastic substrate 11 from the carrier substrate 5 uses the laser apparatus 99 of a high price, the fabrication cost of the OLED display device 70 increases. In addition, since it takes about 10 minutes to about 30 minutes to detach the plastic substrate 11 from the carrier substrate 5 by irradiating the laser beam LB, productivity of making the OLED display device 70 decreases. Further, since the property of the switching TFT and the driving TFT DTr may be degraded or the gate line and the data line may be opened by the laser beam LB, production yield of the OLED display device 70 decreases.